feat(layout): import fx-system alongside global.css

fx-system.css is v7-5's .fx-* design system. global.css continues to
serve the legacy bento components (still used by /about, /services,
/contact, /faq, /blog). No collision because all v7-5 classes are
prefixed .fx-*. No visual change yet — components not wired yet.

Refs: .hermes/plans/2026-06-13_124000-moreminimore-v7-5-migration.md Task 1.2

src/layouts/Base.astro

@@ -1,5 +1,6 @@
 ---
 import "../styles/global.css";
+import "../styles/fx-system.css";
 
 interface Props {
   title: string;